Independent US Food and Drug Administration (FDA) advisors unanimously backed Celltrion’s new Rituxan biosimilar recently, potentially allowing the company to threaten the sales dominance of Roche’s top drug. If approved, this would be the first Rituxan copycat to be granted a marketing greenlight in the US.

Rituxan made Roche more than $4bn in the US in 2017, though the company disclosed recently that some of its patent protections had started to expire through 2018. Rituxan is part of a trio of products, alongside Herceptin and Avastin, under biosim threat, despite generating more than $20bn in sales for the drug giant.

The Celltrion biosim was rejected previously by the FDA, which published a warning about manufacturing concerns in a South Korean plant. Celltrion filed for re-approval in May, saying it expected to have approvals both for the Rituxan biosim and a Herceptin biosim by the end of the year. Novartis is currently aiming for approval of its own biosimilar program, but with progress impeded by the FDA earlier in 2018.

The FDA noted that the Celltrion biosim had no “clinically meaningful differences… in terms of safety, purity and potency.” If approved, Teva would market the Celltrion biosim in the US, with the company “well positioned” to market it, according to Teva’s executive vice president.